Distillation of fine granular solid carbonizable material



Patented May 30, 1933 UNITED STATES PATENT GFFI'CE FRIEDRICH BARTLING, OF MUNICH, GERMANY No Drawing. Application filed November 22, 1928, Serial No. 321,274, and. in Germany December 9, 1927.

United States Patent No. 1,640,502 which was granted to me jointly with Ludwig Honigmann relates to a process for the distillation of fine granular material in a thin layer by heat treatment. The novel feature of that patent consisted in spreading out the material to be treated in layers of a thickness amounting to a fraction of a centimetre.

The advantage thereby obtained consisted in a considerable acceleration of the distil lation process. A substantially better utilization of the heating surface was thereby obtained, and also aconsiderably improved uniformity and quality of the resulting products, particularly of the tar and of the coke or half-coke.

Now the present invention is intended to serve for considerably improving the process described in the said prior specification, especially as regards the production of tar and the expenditure of heat. T he invention is based upon the following considerations:

It is known to be exceedingly important that the distillation gases arising from the granular material, that is, the gases that carry the tar, should not come into contact with parts of the apparatus, the temperature of which is higher than the distillation tem perature, as otherwise cracking of the tar would occur, which would impair its quality'.

Now the highest dew points of the tar in the distillation gases are about 320 C. Hence, if the tars are successfully withdrawn completely from the granular material at a temperature which is only quite a little higher than the dew point of the tars, it is no lou er possible for the quality of the tars to be affected at all, since the formation temperature of the tar is not exceeded at any part of the apparatus.

Now experiments carried out by me on these lines have shown the surprising fact that the diminution in the thickness of the treatment layer within the limits set forth in Patent No. 1,640,502, presents a means for successfuly carrying out the distillation at temperatures ranging from 320 C. up to about 2 millimetres could not lead to this i not more than 380 0., and thereby obtaining the tar in a condition which for the first time really deserves the name of low temperature tar, for the method hitherto adopted of obtaining tar at temperatures of from 470 C. to 520 (3., undoubtedly, already involved a certain degree of overheating for the tar accruing, and this inevitably impaired its quality to acertain degree; yet tars obtained at this temperature have hitherto been regarded as first class low temperature tars.

In any case the spreading out of the material in layers having a thickness down to result, for at such thicknesses, with which I have hitherto preferably worked, higher temperature had to be employed, than hitherto, in odrer to enable the whole of the tars to be Obtained.

In further experiments, however, I have discovered the surprising fact that if the material is spread out in still thinner layers, of a thickness lying between zero and 1% millimetres, the complete extraction of the tars is successfully effected at temperatures between 3lO C. and 350 C.

Accordingly one form of the process for the distillation of fine granular material by heat treatment in a thin layer consists in 80 spreading out the material in layers having a thickness of less than 2 millimetres and employing for the distillation temperatures not exceeding 380 C. From the numerous successful experiments with this method of procedure a new rule has been found, that the less the thickness of the layer, and consequently the size of grain of the material under treatment, the lower is the temperature required for distillation, thereby yielding a corresponding improvement in the quality of the. tar obtained, and also in the percentage yield with a considerably smaller expenditure of heat.

In the distillation of fine granular or pul- 95 verulent coal or similar material, the greatest diificulty arises fromthe great thermal insulating property of the coal, particularly when it is a question of spreading out the material that is to undergo treatment 100 upon a heating surface which is to give up to the spread-out layer of material the necessary heat for carrying out the heat treatment by conduction and radiation. Under 5 these circumstances the parts of the layer of material adjacent to the source of heat are subjected to the thermal treatment under preference conditions, while owing to the poor thermal conductivity of the coal the particles of coal in the upper layers being further removed from the course of heat are shut off from the supply of heat, and consequently considerably are hampered as regards the progress of the treatment. Owing to this there occurs 011 the one hand an overheating of the particles of material lyingnearest to the heating surface, and onthe other hand an incomplete or retarded distillation of the particles in the upper layers. From this again there then follows a lack of uniformity in the solid and gaseous distillation products and in particular the valuable oils, which are sensitive to heat are impaired by overheating.

This disadvantage has already been clearly perceived in the past, but only one possibility was known for obviating it, namely a very energetic agitation and eddying of the pulverulent coal particles, as a result of which the position of the individual coal particles in the layer of material and relatively to the heating surface was continually being changed, so that as uniform a prod not as possible was obtained. This method of procedure, however, had serious disadvantages, particularly with regard to the raising of dust, so that it was to be regarded as a considerable improvement when Patent No. 1,640.502 presented a fundamentally novel way of overcoming the difficulty, by spreading out the material to be treated in layers having a thickness: amounting to a fraction of a centimetre. The disadvantages arising from the thermal insulating action of the particles of coal were thereby so considerably diminished that a substantially better yield and considerably superior distillation products could be obtained.

When treating closely packed masses of pulverulent material a thermal insulating action may occur even in a layer having a thickness of only a few millimetres, and this again brings with it a. lack of uniformity in the treatment of the distillation material.

Accordingly, a further object of the invention consists in combining the spreading out of the material into a thin layer with an earlier method of procedure in such a way as to combine the advantages of both methods.

Hence according to the present invention a process for the distillation of line granular material by heat treatment in a thin .layer, is characterized by the feature that the material is relatively displaced upon the heating surface upon which it has been spread out in layers having a thickness amounting to a fraction of a centimetre.

In this way the following advantages are obtained:

(a) The penetration of heat through the layer is improved owing to the layer being frequently turned over by the relative movement; V (b) By feeding the layer forward upon the heating surface, a heating surface of greater extent can be substantially better utilized.

(0) The discharge of the distillation gases from the closely packed layer of fine granular material is considerably facilitated; and

((Z) By constantly bringing the individv ual grains into contact with fresh parts of the heating surface by pushing them for-- ward upon the heating surfaces, a transmission of larger quantities of heat is obtained at a low temperature.

Obviously it is a matter of indifference whether the heating surface is moved while the layer of material is stationary or wheths er the layer of material is moved while the heating surface is stationary, or. whether both are moved relatively to one another.

The surprising discovery has been made that if the relative movement of the material is slidingly effected upon the heating surface in such a thin layer the whirling up of dust does not take place, but nevertheless the movement of the parts of the material relatively to the heating surface is obtained.

What I claim is:

A method which comprises destructively distilling a layer of coal and completely extracting tar therefrom at a temperature of about 380 C. while stirring the same, the layer of coal being less than 1.5 mm thick.

In testimony whereof I have signed my' name to this specification.

FRIEDRICH BARTLING; 

